Insights into the function and evolution of P450s in plant steroid metabolism.

Numerous cytochrome P450 monooxygenases (P450s) have been known to be involved in the biosynthesis and metabolism of triterpenoids and steroids. This review will survey the oxidative reactions by such P450s and provide insights into the evolution of the steroid-biosynthetic P450 genes in the plant kingdom. Special emphasis is placed on brassinosteroids (BRs), plant steroid hormones, that play essential roles in the regulation of plant growth and development. Several P450s involved in BR biosynthesis and catabolism have recently been characterized by recombinant protein experiments, revealing a new route of the BR biosynthetic pathway.